Smart phone is speedy developed and is basically replacing traditional non-smart phone, the screen size of cell phone is getting larger, the operation mode is also transferred from the traditional push bottom operation mode to the touching operation mode, then the rapidly development of forced touch technology is followed.
Force touch technology is major based on the deformation produced from user's finger pressing the surface of the cell phone screen, and utilizing the force sensor to sense the changes of the pressure, thus to realize the force touch; according to different principle of pressure sensing, force touch technology can be classified into three categories: Piezoelectric type, Pressure resistance type, Capacitance type; pressure resistance type touch technology is simple designed and lowest cost, but pressure resistance type touch technology is restricted by physical limitation, such as low transmittance and lots wired large detecting area caused the loading of the cell phone processor, and pressure resistance type touch technology requires keeping powered status, increases cell phone power consumption, and is easily aged itself then affected the usage lifetime, thus is being phased out; piezoelectric type technology utilize voltage driven to complete touch control, the driven method is similar to the driven method of the liquid crystal display, but also possessed disadvantage of the pressure resistance touch technology, the manufacture process in the cell phone field is not mature enough, and is not widely used.
Capacitance type force touch technology is widely used because of the mature process, high yield, and lower cost; the major implement method of the capacitance type force touch technology is tightly attaching pressure sensor on the middle frame of cell phone or on the backside of the Liquid Crystal display Module (LCM) of the cell phone, as shown in FIG. 1A-1C, according to the different attaching position of the pressure sensor 130, there are three major types of attachment: attached to the middle frame 140 of the cell phone (as shown in FIG. 1B), attached to the bottom surface of the backlight (BL) module bottom frame 1210 of (as shown in FIG. 1A), or attached to the top surface of the backlight module bottom frame 1210 (as shown in FIG. 1C), although the above three methods can achieve the result of capacitance type force touch, but there are other variety electromagnetic signal inside the cell phone, most of the electric signal is a electromagnetic noise signal to the pressure sensor, the sense result of the pressure sensor is then interfered, the force touch sensitivity is reduced, a affected the user experience result.